1. Field of the Invention
The invention relates to silver halide photographic compositions and elements. More particularly the invention relates to such compositions and elements that are spectrally sensitized with novel methine dyes. The new dyes are prepared from novel intermediates, which also can serve as new starting materials for preparing known dyes.
As used herein, the term "methine dye" means a dye comprising two nuclei, at least one of which is a heterocycle containing at least one nitrogen atom, the two nuclei being joined by a methine linkage. which is a conjugated chain of carbon atoms. Methine dyes include such dyes as cyanine, hemicyanine, merocyanine, styryl, allopolar cyanine, complex cyanine, and complex merocyanine dyes.
2. Description Relative to the Prior Art
Methine dyes are generally known as is the use of some of these dyes as spectral sensitizers in silver halide photographic compositions. See, for example, Mees-James, The Theory of the Photographic Process, 3rd ed., N.Y., Macmillan, 1966, Chapter II, pp. 198-230, by L. G. S. Brooker, Sensitizing and Desensitizing Dyes, 65-27328.
Some methine dyes exhibit good water solubility and good compatibility with other emulsion addenda by having acid groups incorporated in the dyes. See, for example, German Offenlegungsschrift No. 2,520,834, published Nov. 27, 1975, and U.S. Pat. No. 3,660,103, issued May 2, 1972.
There is a constant search in the photographic art for new methine dyes to complement those already in use as spectral sensitizers. The present invention provides a new class of methine dyes and a new class of intermediates which are useful in preparing the new methine dyes and known methine dyes. The new methine dyes have been found to be useful as spectral sensitizers for silver-halide photographic compositions and thus provide the photographic chemist with a wider and more flexible choice of spectral sensitizers for any composition or process in which spectral sensitizing dyes are advantageously employed.